This disclosure relates generally to top drive systems and methods for operating a top drive to drill a wellbore. More specifically, this disclosure relates to top drive systems that utilize hydraulic motors to provide the torque needed to rotate a drill string.
A top drive is a system that is suspended in a derrick and used to support and rotate a drill string as well as provide a conduit for the supply of pressurized drilling fluid to the drill string. A conventional top drive system includes an electric or hydraulic motor that is coupled to a drill string. In many systems, the motor is coupled to a transmission, or other gearing, and a short section of pipe, known as a quill. The quill is often coupled to the drill string by a saver sub or may be directly coupled to the upper end of the drill string.
The quill is also in fluid communication with a gooseneck, or other piping, that provides a fluid conduit for the supply of pressurized drilling fluid, or drilling mud, from the rig's mud pumps to the drill string. The drilling fluid flows through the drill pipe and into the wellbore, providing critical functions including, cooling and lubrication of the drill bit, control of wellbore pressures, and cleaning of the wellbore. Drilling fluids are often relatively high density fluids containing suspended solids and other materials designed to improve the drilling process.
Advances in drilling technology have enabled wellbores to be drilled at extreme depths and with the use of long horizontal sections. Both of these types of wellbores necessitate the use of long drill strings. As the length of the drill string increases, the power requirements of the top drive also increases. This need for increased power has been addressed by using multiple motors and/or by increasing the size of the motors being used. As the motors increase in size and/or number the size of the top drive also increases and the supply of power to the top drive motor(s) becomes increasingly challenging. The space available for a top drive is limited by the size of the derrick and high power motors often means larger sized motors.
For top drives with high-power electric motors, additional electrical generators may be needed. Additionally, the cables that supply electric power to the top drive can be prohibitively expensive and cumbersome to manage. Similarly, top drives that utilize hydraulic motors are supplied with dedicated hydraulic power units (including a fluid supply, pump, and power generator). As the power requirements of the top drive increases so do the power requirements, and likely the physical size, of the hydraulic power unit. This can also be problematic on drilling rigs where space is limited.
Thus, there is a continuing need in the art for top drive systems, and methods for operating top drive systems, that address at least some of the issues discussed above.